This invention relates to a motor saw with a motor which is fixed to a casing and which shows an intake port which is connected for decoupling oscillations with a carbureter over a resilient suction hose, the carbureter itself taking its bearing on the casing by means of fixing means.
Such a motor saw is known for example from the document DE-A1-42 34 483.
The carbureter of a motor saw driven by an internal combustion engine (generally a high-speed two-cycle engine) has a considerable influence onto the operating behaviour of the device. Oscillations which come from the moving piston of the motor and act onto the carbureter can result in an irregular fuel supply which endangers a troublefree motor operation. For this reason, it is already known by the prior art for motors which are provided with a carbureter to connect the carbureter with the motor by means of a resilient admission pipe and to additionally create a resilient suspension of the carbureter in the casing. Such resilient suspensions can be made available by a few types of resilient elements, normally made of rubber. Due to such elements, it is possible to obtain an efficient vibration insulation of the carbureter. However, it is a disadvantage of such a suspension that sufficiently resilient elements for the vibration insulation make too important movements of the carbureter possible. A resilient admission pipe is, for example, known from DE-GM 1 762 310 or by SE-PS 8 6022 481-7. Because of the permanently increasing requirements with respect to the reduction of exhaust emissions, a safe motor operation is necessary. An exact adjustment of the carbureter is the condition of low exhaust emissions. Therefore, an oscillation reduced fixation of the carbureter in the suction space would be very advantageous. Furthermore, the fixation of the carbureter should be simple and easy servicing at low cost. From the above mentioned document DE-A1 42 34 483, it is now known to decouple the oscillations from the intake port of the motor by a gas admission pipe made of an elastomer. The carbureter is hinged to the operating area of the saw over a hinge joint in order to be able to move relatively freely in direction of the gas admission pipe.
However, the known hinge joint has different disadvantages. On the one hand, such a connection is comparatively expensive and has a comparatively complicated structure because parts with hinge bores must be produced and the hinge joints must be equipped with corresponding hinge bolts. On the other hand, the mounting and dismounting for servicing is complicated because the hinge bolts must be mounted and locked in the hinge joints with much expenditure and/or unlocked and dismounted. Finally, the hinge joint allows only a limited movability of the carbureter, namely in direction transversely to the hinge joint. On the contrary, a movability in direction of the hinge joint can only be realized with much expenditure if the hinge pins are configured resiliently.
Therefore, it has also already been proposed with DE 197 53 689 A1 a suspension for a carbureter which comprises at least one resilient element which is fixed to the casing and which is connected with the carbureter in order to allow a certain extent of movement of the carbureter relative to the housing, a supporting device limiting the extent of the movement. However, this is bound to disadvantages since, due to the limiting and the thus direct connected support of the carbureter, vibrations are still transmitted in an extent which is not to be tolerated.
Therefore, the aim of the invention is to create a motor saw which avoids the disadvantages of the solution until now and which especially makes possible a vibration free bearing of the carbureter which is simple, easy servicing and which can be realized at low cost.
This aim is achieved for a motor saw of the above mentioned type by the characteristics indicated in claim 1. Due to the renunciation according to the invention to a hinge joint of the carbureter on the casing by means of hinge bolts and the like and to any supporting and delimiting device, the bearing is much simplified. Simultaneously, due to the resiliently articulated one-point suspension, a bearing is obtained which fixes the carbureter in space but which simultaneously decouples it from the oscillations of the motor and of the casing due to the resilient movability in different directions in space. Due to the renunciation to supporting walls and stoppers, an efficient damping device is created. Due to the preferably progressive characteristic curve of the spring constant of the resilient element, it is obtained that higher frequency oscillations as well as oscillations with lower frequency are efficiently damped.
Due to the central arrangement of the damping part and to the chosen one-point fixing, a damping in all planes, i.e. in all directions is achieved.
A first preferred embodiment of the motor saw according to the invention is characterized in that a seat made of an elastic material, especially a resilient bushing made of rubber, is fixed to the casing and that the carbureter is detachably snapped-in with a snap-in part into the seat or the resilient sleeve. The carbureter can thus be very easily mounted by snapping-in into the seat and dismounted by snapping-out of the seat.
A particularly simple snap-in procedure and a very movable bearing result when, according to a preferred further development of the embodiment, the snap-in part is configured as a ball head. Due to the renounciation to snap-in edges, the snap-in part can be snapped in and out with a comparatively low resistance. The ball head acts additonally as a ball joint.
A trunnion which is stuck through the sleeve (not represented) can also be configured instead of the ball head. Thus, the sleeve can be configured with still bigger dimensions (for example air chamber) in order to achieve a special damping characteristic and to simultaneously guarantee a xe2x80x9cfixedxe2x80x9d adjustment (fixing).
A further embodiment of the resilient sleeve allows a configuration of the damping element which is much more resilient. Due to the very resilient configuration, the mounting procedure of the damping element not together with the suction flange is possible. Therefore, the damping element is separated from the suction flange and preliminarly placed in the mounting sequence. The suction flange is snapped-in later. For the configuration of the damping element, due to the ellispoidal form a very xe2x80x9csmoothxe2x80x9d characteristic curve in direction of the carbureter bottom can be obtained. On the contrary, in the crankshaft axle direction, the spring characteristic will turn out harder. Thus, the whole suction system can be positioned very smoothly but still axially safe.
Further embodiments result from the depending claims.